I've got a beater, an '89 Mitsu Mirage, with a trace leak in the heater core-slight smell when in use. What are my options for an additive leak fixer? I want to fix it, but without gumming up the whole system. Thanks ahead of time.
I personally have used those ones in powder form (looks like metal with little fibres in it) to stop a weeping head gasket, and a hairline crack in a block...worked well.
I've used tins of Bars-leak a couple of times on seriously holed radiators as a "get you home" concept, probably a bit extreme for a "smell" as opposed to wet carpet.
I think the Bars dry pellets might work for you.
But please only use them temporarily.